1. Field of the Invention
The present invention is in the field of re-treaded tires.
2. Description of the Related Art
When tires become worn, they can be restored with new tread. Large truck tires are typically retreaded as part of a routine tire-management program. The carcass of a truck tire is expected to last several hundred thousand miles and be amenable to having a new tread adhered to it several times. New truck tires are quite expensive and are therefore bought with the expectation that their high initial costs are offset by the long service life of the carcass and the low comparative cost of retreading.
A variety of procedures and different types of equipment are available for use in recapping or retreading pneumatic tires. One of the first steps in retreading a worn tire is to remove existing tread material from the tire carcass by a sanding procedure known as buffing. Next a layer of what is known as “cushion gum” is applied to the carcass. This layer of extruded, uncured rubber may be stitched or adhesively bonded to the carcass. Next, a tread layer is applied atop the layer of cushion gum. In the cold recapping process, the tread layer is cured rubber, and has a tread pattern already impressed in its outer surface. The tire is then placed in an autoclave, and heated under pressure for an appropriate time to induce curing of the gum layer, and binding of the gum layer to the inner or sole side of the tread layer and the carcass. The term “cure” refers to the formation of cross-links between the elastomer molecules in the rubber compound. It is further noted that there are various methods of bonding the tread layer to the carcass such as the use of adhesives, bonding agents, cushion gums, etc., and that all of the methods known in the art are included when referring to the term “bonding interface”.
A common problem with tires, including retreads, is that as the tire wears, the traction-providing elements also wear, until eventually the elements are substantially worn away. The result can be a significant reduction in traction for the worn tire. Efforts have been made to develop a tread layer that has tread elements cut into the sole side (the side opposite the tread side) of the tread layer. The term “tread elements” refers to sipes, lateral grooves, and/or longitudinal grooves or any other void formed in the tread. The tread elements molded into the sole side of the tread layer appear as the tire wears, giving improved worn traction over the life of the retread and allowing the tire to be removed from service later in life. One problem identified in these earlier efforts is that a stress riser is created at the sharp edge of the interface of the tread elements/bonding interface that provides a crack initiation point allowing the tread to peel away from the tire carcass.